1. Field of the Invention
This invention relates to an apparatus for reproducing digital data. This invention also relates to a method of reproducing digital data.
2. Description of the Related Art
It is known that parity information for error correction is added to digital data before the digital data is recorded on a recording medium. During the reproduction of the digital data from the recording medium, the parity information is used in correcting an error or errors in the reproduced digital data.
In a prior-art recording and reproducing system, first data blocks (referred to as the data blocks "A" hereinafter) such as transport packets conforming to the MPEG standards are converted into second data blocks (referred to as the data blocks "B" hereinafter) differing in size from the data blocks "A", and the data blocks "B" are recorded on a recording medium. During playback, the original data blocks "A" are reconstructed or recovered from corresponding reproduced data blocks "B".
In the prior-art system, to enable the reconstruction of the data blocks "A" during playback, the order of the blocks "A" of input data is maintained in a sequence of the data blocks "B" which are recorded on the recording medium.
Generally, input data has a variable transmission rate. It is known to add dummy data blocks to input data to compensate for a variation in the transmission rate of the input data. Then, the dummy-added input data is recorded on a recording medium block by block. In this case, the data blocks recorded on the recording medium are of two types corresponding to the original input data and the dummy data respectively.
It is also known that special data for special playback such as high-speed playback is added to input data before the input data is recorded on a recording medium block by block. In this case, the data blocks recorded on the recording medium are of two types corresponding to the original input data and the special data respectively.
During the recording of data blocks "B" of plural different types on a recording medium, the header of every data block "B" is loaded with an identification signal representing the type of the data block "B". During a given playback process on a recording medium storing data blocks of plural different types, only data blocks of a desired type are extracted from reproduced data blocks, and are outputted as a desired reproduced signal. Specifically, the identification signal in the header of every reproduced data block is examined to detect the type thereof, and thereby the data blocks of the desired type are discriminated from the reproduced data blocks of the other types.
During playback under some poor conditions, an error rate of reproduced data is great so that the order of reproduced data blocks "B" deviates from a correct order for the reconstruction of data blocks "A". In this case, a sequence of the reproduced data blocks "B" tends to contain wrong data blocks. Decoding the wrong data blocks "B" into corresponding data blocks "A" results in a reduction in quality of information recovered from the reproduced data blocks "B". The wrong data blocks "B" tend to break operation of an MPEG decoder.